Polygon:

- Added async methods to polygon.
- The `requests` library is no longer required, with `urllib` being used instead.
- Added the `get_bar_data` function, which returns a dataframe of aggregate data from polygon.
- Opened up the `subscribe` and `unsubscribe` functions

Enhancements:
- Tables will now scroll when the rows exceed table height.

Bugs:
- Fixed a bug preventing async functions being used with horizontal line event.
- Fixed a bug causing the legend to show duplicate lines if the line was created after the legend.
- Fixed a bug causing the line hide icon to persist within the legend after deletion (#75)
- Fixed a bug causing the search box to be unfocused when the chart is loaded.

docs/source/examples/toolbox.md

@@ -0,0 +1,73 @@
+# Toolbox with persistent drawings
+
+To get started, create a file called `drawings.json`, which should contain:
+```
+{}
+```
+___
+
+
+
+```python
+import pandas as pd
+from lightweight_charts import Chart
+
+
+def get_bar_data(symbol, timeframe):
+    if symbol not in ('AAPL', 'GOOGL', 'TSLA'):
+        print(f'No data for "{symbol}"')
+        return pd.DataFrame()
+    return pd.read_csv(f'bar_data/{symbol}_{timeframe}.csv')
+
+
+def on_search(chart, searched_string):
+    new_data = get_bar_data(searched_string, chart.topbar['timeframe'].value)
+    if new_data.empty:
+        return
+    chart.topbar['symbol'].set(searched_string)
+    chart.set(new_data)
+    
+    # Load the drawings saved under the symbol.
+    chart.toolbox.load_drawings(searched_string)
+
+
+def on_timeframe_selection(chart):
+    new_data = get_bar_data(chart.topbar['symbol'].value, chart.topbar['timeframe'].value)
+    if new_data.empty:
+        return
+    # The symbol has not changed, so we want to re-render the drawings.
+    chart.set(new_data, render_drawings=True)  
+
+
+if __name__ == '__main__':
+    chart = Chart(toolbox=True)
+    chart.legend(True)
+
+    chart.events.search += on_search
+    chart.topbar.textbox('symbol', 'TSLA')
+    chart.topbar.switcher(
+        'timeframe',
+        ('1min', '5min', '30min'),
+        default='5min',
+        func=on_timeframe_selection
+    )
+
+    df = get_bar_data('TSLA', '5min')
+
+    chart.set(df)
+
+    # Imports the drawings saved in the JSON file.
+    chart.toolbox.import_drawings('drawings.json')
+    
+    # Loads the drawings under the default symbol.
+    chart.toolbox.load_drawings(chart.topbar['symbol'].value)  
+    
+    # Saves drawings based on the symbol.
+    chart.toolbox.save_drawings_under(chart.topbar['symbol'])  
+
+    chart.show(block=True)
+    
+    # Exports the drawings to the JSON file upon close.
+    chart.toolbox.export_drawings('drawings.json')  
+
+```